In pressurized water reactors (PWR), boiling water reactors (BWR), and other types of nuclear reactor designs, various high energy lines such as those associated with a steam generator system may be subject to pipe break. The pipe break may lead to jet impingement, pipe whip, and potential impact loads. A typical solution to mitigate or avoid the effects of the pipe break may involve attaching a pipe whip restraint to a building or other large structures to absorb the energy of the pipe breaks. For example, the pipe whip restraint may be attached to a one-foot thick concrete bioshield wall. In addition, jet impingement shields may separately be provided to protect various equipment form the jet forces, which can exceed well over 15,000 pounds of thrust.
Pipe whip restraints comprising U-bolts may be configured to dampen and absorb the kinetic energy of bursting pipes in emergency cases. Pipe whip restraints assembled in angular arrangements may be configured to absorb the forces, and the direction of the absorbed force can be determined by the particular arrangement of the U-bolts. Other types of known pipe whip restraints may comprise shock absorbers, rigid struts, and pipe clamps.
A shock absorber (or snubber) may be configured to form a semi-rigid restraint between the pipe and the structure during a seismic or dynamic event. The resulting energy in the pipes may be absorbed and transferred to the structure up to a maximum rated load, and when above that, the forces may be transformed into deformation energy by the energy absorber.
The shock absorber may comprise an adjustable free stroke to allow for slight thermal movement of the pipes. Piping may be displaced within the adjusted range of the free stroke, provided that the permissible stresses are not exceeded. As one of the most frequent causes of failure in shock absorbers is wear, these types of pipe whip restraints may be limited to applications where little operational movement is to be expected at the load application point.
Struts may form rigid restraints from one attachment point to another so as not to allow any axial movement. The struts may comprise ball bushings that form rigid connections between the pipe and the structure. Some limited angular movement may be allowed by the struts; however, from a practical matter, rigid struts are not acceptable when any significant operational movement of the pipes must be accounted for.
Pipe clamps may comprise a solid upper yoke with integrated connection bracket and, depending on the load range, one or two U-bolts with inlay plate. The bracket may be welded to the upper yoke. Instability caused by friction pipe clamps may result from creep characteristics of preset metals and, if the clamp design is too soft, the necessary stiffness may not be attained. Some clearance in the pipe clamps may be provided to accommodate minimal displacement of the piping system.
In addition to the various limitations discussed above, known pipe restraint systems require placement of the pipe whip restraints at or near a building or other large physical structure, and the requisite structure may not be located at an ideal place for attachment. The attachment of the pipes to the super structure may result in a substantial transfer of seismic or other dynamic forces between the structure and the pipes, and may operate to change the functional behavior or response of the pipe system. Additionally, even if the known pipe restraint systems are successful in keeping the pipes themselves from damaging other components, the resulting jet stream that escapes out through the pipe rupture may nevertheless cause resultant damage to the surrounding components.
This application addresses these and other problems.